Why gear pumps for thick fluids
An external gear pump traps the fluid between the teeth and the casing and carries it from suction to discharge. Nothing is accelerated, nothing is thrown by a vane: the fluid is displaced. That is why the flow stays constant when back-pressure rises, why the pump is self-priming, and why viscosity — the enemy of centrifugal pumps — helps rather than hurts.
Low speed is the rule
With very viscous products the gears need time to fill. A pump that turns too fast cavitates: it gets noisy, vibrates and delivers less than its rating. On molasses, resins, heavy oils or bitumen we usually choose a larger pump turning slower, often with a gear motor. It costs a little more and lasts much longer.
Suction decides everything
A gear pump does not pull a thick fluid; the tank pushes it in. Short, wide suction lines, a flooded inlet and the pump close to the tank are worth more than any extra horsepower. Every enquiry form on this site asks for the suction conditions for this reason.
Fluids we handle every day
Molasses, bitumen, heavy fuel oil, glucose syrup, honey, chocolate, epoxy resin, polyol, silicone, castor oil, grease — and more than 190 others in the A–Z list.
Frequently asked questions
What is the maximum viscosity a gear pump can handle?
There is no single limit: it depends on pump size, speed and suction conditions. The thicker the fluid, the larger and slower the pump. Send us the viscosity at pumping temperature and we size it.
Is a gear pump self-priming?
Yes. External gear pumps are self-priming, but with very viscous fluids a flooded suction is still strongly recommended.